Early on in our transatlantic phone conversation, it suddenly becomes unclear whether I’m chatting to Irvine Welsh or Frank Begbie. When I ask whether he might well be the busiest man in Scottish culture right now, the response comes over loud, clear and mildly threatening: ‘I’m hoping to get onto your guys’ top 100 creative Scots next year, cos I didn’t even make the list last year, eh? It’s easy being busy but if it’s all a lot of shite, it doesn’t really count for much.’ Had he chucked in a menacing ‘likesay’, I would have been truly thankful for the ocean that separated us.

But busy he most certainly is. Our chat is primarily to discuss Skagboys, the prequel to Trainspotting, but he uses the time to mention some other projects he’s involved with stateside. These include a stage version of Trainspotting set in Kansas City, the US publication of Skagboys in September, and an HBO drama about Romany-Irish bare-knuckled fighters and the novel he’s currently working on: ‘It’s set in Miami Beach about two women who are obsessed with each other; one is a fitness trainer, the other’s an artist, so this one is a very American book. But I also want to do a book about post-Bawbag Scottish society.’ Within our allotted time, we don’t even get round to mentioning this year’s fi lm versions of Filth and Ecstasy, starring, respectively, James McAvoy and Kristin Kreuk.

He may now spend much of his residency time in Miami, but it seems that while you can take the boy out of Leith … ‘I’m there all the time when I come back to Edinburgh, either in the City Limits or Robbie’s or even the big Wetherspoon’s, I’m always on that kind of path.’ And does his path include strolling up the Walk past that massive poster of his beaming phizog beside the slogan ‘I ❤ Leith’? ‘I love drawing people’s attention to it: “That’s me, that’s me!” No, it’s brilliant though. I only thought it would last a few seconds; I didn’t realise it would be a permanent fixture.’

Irvine Welsh’s status as a permanent fixture and fitting on the Scottish literary landscape was assured from the moment Trainspotting was first discussed among the Edinburgh lit pack. Kevin Williamson, his Leith buddie and fellow member of the Twitterati (‘It’s the only way I can keep up with him and Tam Dean Burn these days’), famously dubbed it as ‘the best book ever written by man or woman’, while Danny Boyle later turned it into an epoch-defining Britflick. Metropolitan critics were not quite so taken with Welsh’s vivid depiction of a pervasive drug subculture written largely in a raw Embra vernacular, in particular when a pair of 1993 Booker Prize judges apparently threatened to resign their duties had the novel made it anywhere near the shortlist.

In 2002, Welsh reunited the gang for Porno, in which Sick Boy wielded his powers of manipulation to make waves in the adult movie business, Spud attempted to pen a history of Leith, Renton flitted between Edinburgh and Amsterdam, and Begbie spent the entire book trying to work out who had flooded him with gay porn during his period at her majesty’s pleasure and plotting horrible vengeance upon Renton who had fled at the end of Trainspotting with his cash.

The finale of Porno (a semi-comatose Begbie reeking of urine and retribution, rousing Carrie-style to scare the bejesus out of a midconfessional Sick Boy) certainly left it wide open for a further instalment of these radge-own adventures. Welsh is not ruling out the prospect: ‘You can never really draw a line under it because the characters keep coming back to you; they gatecrash into the consciousness whether you want to write about them or not and you get curious about them.’

Certainly, Welsh’s curiosity was suitably piqued for him to dip into his characters’ early encounters with rough sex, hard drugs and rock’n’roll – all three even merging in Spud’s ill-fated encounter with ageing Dutch chanteuse Claudia Rosenberg, ending with him fleeing the Caledonian Hotel, armed with only two silver room-service trays to shield his modesty. But as much as Skagboys is the story of a clutch of Edinburgh boys losing their way, it’s equally a novel about the viciously divisive decade that was the 1980s as Thatcherism and the free market ran riot around the nation, riding roughshod over communities (mining villages, inner cities, Scotland) which were viewed as surplus to monetarism’s requirements. The book begins with Renton’s rehab diary recalling the time he joined his father on the picket line at Orgreave and faced down a politicised and brutal police operation.

‘It’s more of a cause-and-effect historical novel about the 80s rather than just exploring a subculture, which Trainspotting did. You’ve had the hateful figures of Blair and Cameron to take Thatcher’s place. As she is old and feeble now, there’s a tendency to see her as this nice old lady who used to batter people with her handbag. But the 80s was a very bitter time and really made us the nation we are now.

‘Unlike Europe, we chucked in any pretensions of building a social order and decided to become the 51st state of America where the market remained supreme and where things like a universal comprehensive education system and a general welfare state and a socialistic aspiration to build a better society were all shelved. They may never come back despite the insipid window dressing the Labour Party have tried from time to time; it was a time when this consensus was first made by all the main parties.’

But Welsh sees one upside to that era’s social destructiveness. ‘It was the last time we had a proper indigenous British culture which had gone back to the teds through to mods and punks; in the 80s we had acid house and casuals. The 90s was a decade of mundane market-consumer nothingness where there was nothing coming up from the streets; you just had someone in an office deciding what was cool.’

Given that the interview started with shades of Begbie, we end it chatting about who, among his Skagboys crew, Welsh would feel most happy sharing a pint with in Robbie’s or City Limits. ‘Spud is the most loveable but you’d probably get a bit exasperated with him eventually. With Sick Boy, I’d be watching my wallet all the time, and I’d be a bit nervous sitting down with Begbie. I’d have to say probably Renton as you’d get quite a varied conversation out of him. But they’re all me, as are the extended characters; Alison and the guy in the suit she’s shagging are as much me as Renton, Begbie and Sick Boy. You have to inhabit every character you write and find bits of you to put into all of them to make them work.’

Skagboys is out now, published by Jonathan Cape. Irvine Welsh’s Ecstasy is on general release, out now.